The Operational Linescan System (OLS) was the primary experiment on the DMSP Block 5D spacecraft. The purpose of this experiment was to provide global, day/night observations of cloud cover and cloud temperature measurements to support Department of Defense requirements for operational weather analysis and forecasting. The OLS employed a scanning optical telescope driven in an oscillating motion, with optical compensation for image motion, which resulted in near-constant resolution throughout the sensor field of view. The radiometer operated in two ("light" and "thermal") spectral intervals -- (1) visible and near infrared (0.4 to 1.1 micrometers) and (2) infrared (8 to 13 micrometers). The radiometer produced, with onboard processing, data in four modes -- LF (light fine) and TF (thermal fine) data with a resolution of .56 km, and LS (light smoothed) and TS (thermal smoothed) data with a resolution of 2.8 km. There were three onboard recorders, and each had a storage capability of 400 min of both LS and TS data or 20 min of LF and TF data. For direct readout to tactical sites, the experiment was programmed so that LF and TS data were obtained at night. The infrared data (TF and TS) covered a temperature range of 210 to 310 deg k with an accuracy of 1 deg c. The LS data mode provided visual data through a dynamic range from full sunlight down to a quarter moon. This mode also automatically adjusted the gain along scan to allow useful data to be obtained across the terminator. Additional information on this experiment is contained in the report, 'Primary Optical Subsystems for DMSP Block 5D,' D. A. Nichols, Optical Engineering, 14, No. 4, July-August 1975.